Contemporary robotic work tools are designed to operate in areas with obstacles, permanent and temporary. One example being a garden with a fountain in it. The fountain may not be marked with a boundary marker and the robotic work tool should be able to detect that it has collided with the obstacle so that it can continue to operate in another direction instead of coming to a standstill while pushing against the fountain. The collision detection thus influence an operating pattern of the robotic work tool and affects the ongoing operation (such as through a change in direction), but does not discontinue the operation.
Furthermore, many robotic work tools, such as lawnmower robots, carry work tools, such as cutting blades, that may injure or cause damage if not handled properly. A common problematic situation occurs when a user lifts a robotic work tool to move it from one area to another, or perhaps just to change direction, when the user may become exposed to the work tool. It is thus of importance for safety reasons that the robotic work tool is able to detect that it is being lifted, also for partial lifts, and at least temporarily deactivate any work tool. The lift detection thus, at least temporarily interrupts the operation of the robotic work tool and it is important to distinguish between these two detections.
For these reasons many robotic work tools are arranged with both collision detection sensors and lift detectors. Having two sensors for each action results in that an robotic work tool needs to have many detectors especially to be able to detect collisions in all directions and also to detect partial lifts in different parts or corners of an robotic work tool.
One manner of detecting collisions is disclosed in the international patent application published as WO 03/103375. The application discloses a self-propelling device, preferably a self-propelling lawn-mowing robot comprising at least a control and navigational control system that in conjunction with outer influence on the device, for instance collision with an object, at least by information from one or several sensors placed in or on the device, controls the movements of the device across a surface area. The device is designed so that at least a first part of the device moves in relation to the device's remaining parts in conjunction with the outer influence. The device is so designed that the first part of the device moves in relation to the device's remaining parts in conjunction with outer influence. The self-propelling robot comprises a sensor that detects the movements of the first part without being in contact with the first part. Two main embodiments are disclosed with reference to (mainly) FIGS. 11 and 13. The first embodiment (FIG. 11) is directed at detecting collisions as is clearly stated on page 6, line 11. The second embodiment (FIG. 13) is directed at detecting lifts (or crossing a hollow) as is clearly stated on page 7, lines 10-12. In the first embodiment the sensor arrangement is arranged close to the rear wheels. In the second embodiment the sensor arrangement is arranged close to the front wheels (compare with FIG. 10 for location of components). Thus, the disclosure teaches to use one setup to detect a collision and one setup to detect a lift/crossing a hollow. These two embodiments would not be possible to combine without significant modification.
Even though the problems above have been discussed for lawnmower robotic work tools, the same or similar problems exist also for other robotic work tools.
There is thus a need for a manner of detecting both collisions and lifts without requiring too many sensors.